Dissertation / PhD Thesis

FZJ-2015-01523

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Spannungsinduziertes Versagen in Hochtemperaturschichtsystemen

Nordhorn, C. (Corresponding Author)FZJ*

2014
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-016-6

Please use a persistent id in citations: http://hdl.handle.net/2128/8446

Abstract: Ceramic components in high-temperature coating systems are prone to stress-induced failure because of thermal mismatch and system specific degradation processes. Lifetime models are developed, in order to identify the underlying mechanisms of system failure and to assess the coating system reliability. A probabilistic lifetime model was developed for calculations of the durability of atmospherically plasma sprayed thermal barrier coating systems under thermo-cyclic loading. The model algorithm includes finite element analyses of thermally induced stress fields in consideration of thermally induced oxide scale growth, sintering of the ceramic topcoat, stress relaxation, and microstructural features of the ceramic-metal interface. To reduce the computing time, the interface of two-dimensional models was approximated by periodic functions, which are parameterized based on experimentally determined surface roughness parameters. The results of stress measurements in grown oxide scales by photo-stimulated luminescence-spectroscopy validated the implementations of mechanical boundary conditions, material parameters, and the methodology of microstructure approximation for the subsystem without topcoat. Lifetime relevant stress field distributions calculated on the basis of interface approximation functions were found to be in accordance with stress distributions from three-dimensional finite element analyses with realistic interface structures, which were imported from topography measurements. The lifetime model requires a calibration by presetting an experimental lifetime distribution. The associated cycle dependent calibration parameter re ects the effect of fracture toughness increase for increasing crack length. The calculated stress field distributions are employed in fracture mechanical analyses of subcritical crack growth. A comparison of the transient energy release rate with its crack length dependent critical value results in cumulative distribution functions for the probability of system lifetime in dependence of the cycling conditions. Calculated lifetime expectation values and standard deviations were found to be in accordance to experimental lifetimes determined as a function of interface temperature. The stress field inversion rate directly correlated to oxide scale growth rate was identified as main failure mechanism. Sensitivity analyses were conducted with regard to further parameter effects on the lifetime. The lifetime model algorithm was abstracted and applied to the stress induced failure of chromium evaporation barriers in stacks of solid oxide fuel cells providing a conceptual modelling approach.

Keyword(s): Dissertation

Note: Ruhr-Universität Bochum, Diss., 2014

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 122 - Power Plants (POF2-122) (POF2-122)

Appears in the scientific report 2014

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Database coverage:

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